Not Applicable
Not Applicable
1. Field of the invention
This invention pertains to waste heat power generation systems and particularly to waste heat-generating systems that utilize refrigerant gasses as the waste heat recovery medium
2. Description of related art
Electrical generation facilities fall into three main types: large-scale plants that use coal, oil or nuclear power to generate steam to drive a turbine-generator set; moderate scale plants that use natural gas to fire turbine-generator sets; and small scale plants that use various fuels and methods to generate electricity. All of these plants operate on thermodynamic cycles that are less than forty-percent efficient, which results in the production of large quantities of so-called waste heat. Currently, much of this heat is exhausted into the atmosphere or waterways through exhaust stacks and cooling towers. As energy costs began to rise over the last twenty years, engineers have studied the uses for waste heat as a way to return more of the economic value from the energy input into the system. A simple example of such a system is a gas turbine. The exhaust gas of the turbine can be passed through a heat exchanger to make steam that can drive a steam turbine to produce additional electrical output. Another example is a diesel generator that has a heat exchanger on its exhaust that can be used to heat buildings.
Despite these improvements in the use of waste heat, these systems do not fully utilize all of this energy, because they are only designed to recover so-called xe2x80x9chigh qualityxe2x80x9d waste heat, typically at temperatures significantly above that at which steam condenses and loses it""s latent heat of vaporization. As such, those systems do not have the most efficient overall heat use.
The challenges of recovery and utilization of this xe2x80x9cwastexe2x80x9d heat, with a large reduction in the quantity and nature of particulate matter and noxious gasses vented to the atmosphere are the subject of this invention.
In one particular case, the engine exhaust gas flow is condensed and scrubbed, with utilization of exhaust, radiant, and jacket water waste heat, which, when converted from heat energy to mechanical energy, makes possible a significant reduction in fuel usage per unit energy.
Thus, the instant invention is here presented as an electrical generation system, in this particular implementation, that fully integrates heat utilization during the process of electric power generation with a maximum conversion from heat energy to mechanical energy with minimal energy losses and environmental pollution. As such, the energy efficiency of the entire system is much improved.
While the principles are directly applied in this one instance, the system is scalable in nature and is easily retrofit to any existing facility where there is a heat energy source with an energy density of sufficient magnitude.
The system is contained within a thermodynamic boundary. Energy is input to the system in the form of diesel fuel and heat contained in the combustion air. Electric power, exhaust gas flow cooled to near ambient atmospheric temperature, sound and vibration, and water exit the boundary. An energy sink is provided by a turbine (through connection to the generator and its subsequent connection to a sufficient electrical load), where heat energy is converted to rotative mechanical energy used to power the generator.
There are four interconnected systems:
1) A diesel engine that provides motive power for the generator and is the primary source of waste heat for the recovery system""s use;
2) a primary, high temperature refrigeration system used to supply energy to the recovery turbine;
3) a secondary refrigeration system to provide proper operating parameters for the recovery turbine exhaust, and
4) a water handling system.
The high temperature refrigerant selected is R 22, a common hydroclorofluorocarbon, and is selected for the following characteristics:
1) a critical temperature at or slightly below the boiling point of water at atmospheric pressure;
2) a superheated gas inlet temperature and pressure within conventional turbine operating and manufacturing capabilities;
3) vapor characteristics that allow for condensation at or above atmospheric pressure, but below 75 psia, at xe2x88x9220xc2x0 F.;
4) a low latent heat of vaporization to minimize system support complexity;
5) a high molecular mass;
6) environmentally friendly;
7) a substance that is readily available;
8) a system architecture within the capabilities of those who are semiskilled in refrigeration systems operation and repair techniques; and
9) a large superheat value when heated to between 250xc2x0 and 350xc2x0 F.
The refrigerant R 22 embodies all of these criteria, with the exception of 4.
A heat engine, embodied as an axial turbine, converts heat energy contained in the R 22 vapors to mechanical energy output from the turbine shaft.
To accommodate the condensing requirements of R 22, and to permit conservation of the energy contained as the latent heat of condensation of the turbine vapor discharge, a separate refrigeration system is needed to create a condensing environment for the vapors exhausted from the turbine. An ammonia subsystem is used for this purpose, and for the following reasons:
1) a xe2x88x9220xc2x0 F. evaporator temperature obtainable at or above atmospheric pressure;
2) a high latent heat of vaporization to minimize system requirements;
3) a condensing temperature within the range of commercially available evaporative condensers when radiating the latent heat of condensation to ambient air;
4) environmentally friendly;
5) a substance that is readily available; and
6) a system architecture within the capabilities of those who are semiskilled in refrigeration systems operation and repair techniques.
The ammonia system is used to anchor the recovery turbine outlet (R22 condensing) temperature at xe2x88x9215xc2x0 F.
The water system is used to cool and condense the diesel engine exhaust gas flow, to supply the evaporative condensing system with evaporant, and to act as a reservoir for the water that results from the oxidation of hydrogen and hydrocarbon fuels. Extraction and further conversion of combustion by-products such as carbon dioxide, nitrous oxides, sulfur oxides, unburned hydrocarbons, carbon, other particulate matter, as well as important emergency system shut down functions, are also enabled by this reservoir.
As is further described below, the separate systems identified are thermodynamically interconnected, so that one system gives up heat to another system at particular places where such interconnecting improves or enables system operation and/or system performance goals.
System Operational Overview
A diesel engine is used to rotate an electric generator to produce power. The engine jacket water is cooled by a heat exchanger. The operating fluid used to cool the engine jacket water is R 22. Here, R 22 is converted from a high pressure, high temperature liquid to a high pressure, superheated vapor as it absorbs the heat rejected to the water cooling the engine.
The diesel engine exhaust is routed to an exhaust gas condenser where water is used to cool and condense the superheated gasses and other constituents that make up the exhaust flow. The water used to cool and condense this flow is maintained at an appropriate operating temperature by using a heat exchanger. The operating fluid used to cool this water is R 22. The R 22 is converted from a high pressure, high temperature liquid to a high pressure, superheated vapor as it absorbs the heat rejected to the water cooling the exhaust gas flow within the exhaust gas condenser.
The combined R 22 superheated flow from these two heat exchangers is routed to the recovery turbine primary inlet connection.
In this particular implementation, the recovery turbine used is an impulse turbine of axial construction, with two energy inlet connections:
The first is for the superheated vapor flow coming from the heat exchangers.
The second is used to both reheat and increase the R 22 vapor flow rate in a secondary stage of the turbine, which is discussed below.
The recovery turbine, in this particular implementation, is free running and directly connected to the second input shaft of the main electric generator. With the diesel engine fuel control maintaining a constant system synchronous speed, the engine specific fuel consumption for a given energy output will decrease by an amount equal to the rotating energy thermodynamically converted from heat energy to mechanical energy and output by the turbine.
To condense the exhausted R 22 vapor exiting the turbine""s last stage, it is necessary to remove an amount of heat equal to its latent heat of condensation at a specific temperature and pressure relationship.
This condition is created by using an ammonia refrigeration system. The condensing temperature for the R 22 vapor is set, in this particular implementation, at xe2x88x9215xc2x0 F. The latent heat of condensation of the R 22 is absorbed by ammonia evaporation and expansion. The evaporated ammonia, and the energy it contains, is input to the ammonia compressor suction, where the ammonia vapor""s pressure and temperature relationship is changed. The energy used by the compressor to accomplish this change is contained within the compressor discharge flow.
The ammonia compressor discharge flow is routed through an evaporative condenser where most of the latent heat of condensation is removed by the evaporation of water within the evaporative condenser. The diesel engine combustion air intake creates an airflow that enhances the evaporation of water by and within the evaporative condenser. The energy entrained within this flow becomes part of the heat energy input to the diesel engine. The mass of the intake airflow is also increased by an amount equal to the weight of the water evaporated. This alters engine operating and combustion characteristics, described below.
The exiting ammonia flow is now routed to a heat exchanger in the R 22 liquid line. Here, more heat energy is removed from the ammonia compressor discharge and is imparted to the liquid R 22. This raises the specific heat value of the R 22 liquid flow, while removing more of the latent heat of condensation from the ammonia compressor discharge. This preheating of the R 22 liquid decreases the net refrigeration efficiency, per unit mass, of the R 22 at the heat exchangers for the engine and exhaust gas condenser. This increases the net flow rate of R 22 through the recovery turbine.
Heat rejected from the generator and other system components within the thermodynamic boundary is also contained within this airflow. The elevated temperature of the ambient air, caused by radiated heat from system auxiliaries"" operation, increases the evaporation rate of water by increasing the intake air temperature.
It is an object of this invention to produce a generation system that uses a minimal energy input to produce the maximum energy output.
It is another object of this invention to produce a generation system that uses waste heat produced as a useful element in the generation cycle.
It is a further object of this invention to produce a generation system that uses an integrated set of subsystems that maximize the efficiency of the generation system.
It is yet a further object of this invention to produce a generation system that enables recovery and reduction of environmental pollutants being emitted into the atmosphere as a result of the generation of electricity.